Diarrhea When Dieting – Causes and Remedies to Stop It

Alterations in bowel habit are not uncommon when dieting or fasting, especially for long periods of time. Some people may experience constipation. Others may experience diarrhea. It is important to understand why these alterations occur when dieting in order to prevent it as far as possible. However, when diarrhea with dieting does occur then it should be assessed and treated by a doctor. Diarrhea can lead to serious and even life threatening complications.

Is diarrhea normal when dieting?

Any change in dietary habits can result in short term changes in bowel habit, such as constipation or diarrhea. This may occur with fasting or any other change in diet, apart from dieting with the purpose of losing weight. Increased physical activity, like exercise, which may be part of a weight loss program can also contribute to diarrhea.

Diarrhea should never be considered as normal bowel habit. However, it is not entirely uncommon when dieting and most of the time it is not serious.  The diarrhea may only last for a short period and pose not major risk to a person’s health. Nevertheless there is a risk when diarrhea is severe and/or prolonged.

It is important to note that dieting should not be considered synonymous with starvation. A well planned diet for weight loss should not severely restrict food intake or lead to deficiencies as may result with starvation. With severe restriction of food as is seen in starvation, constipation is more likely to occur

Read more on constipation when dieting.

Causes of Diarrhea When Dieting

Sometimes the cause of diarrhea when dieting may not be due to the dietary changes. Instead it may be associated with other causes of diarrhea such as infections or flareups of chronic bowel conditions that present with diarrhea. It is therefore important to not only focus on the diarrhea but to find the exact cause of the diarrhea. Some of the possible contribute factors to diarrhea when dieting has been discussed below.


Excessive intake of high fiber foods (fruit, vegetables and wholegrains) as well as fiber supplements are not an uncommon approach to dieting. Fiber is indigestible and provides bulk when it absorbs water which may be used to make a person feel full with small amounts of food. Ultimately this reduces food intake.

High fiber intake with some diets can increase the frequency of bowel movements and even contribute to diarrhea. Normally fiber is not absorbed in the gut and helps to bulk and bind the stool. A lack of fiber is a common cause of constipation. However, a very low fiber intake especially with a liquid diet can also lead to diarrhea.


Increased fluid intake, particularly water, is another common component of many weight loss diets. This can speed up bowel motility and therefore increase bowel movements. However, if a high fluid intake is maintained especially when there is insufficient solid food consumption then it can lead to diarrhea.

Furthermore water alone without electrolytes may not be absorbed efficiently. As a result the water remains in the bowels and can contribute to watery stool. Conversely, fluids with very high concentrations of electrolytes may draw water from the body into the bowels and result in diarrhea.


Some diets recommend a high fat intake often with a high protein intake and little to no carbohydrates. These types of diets can also affect the bowel habit. Sometimes fat cannot be properly digested when consumed in large quantities, either due to disturbances in fat-digesting enzymes (lipase) or bile that emulsifies fats.

As a result the fat remains in the bowels. It disturbances the osmotic gradient between fluid in the bowels and fluid in the tissue spaces. This can cause diarrhea. In addition the stools are fatty or greasy in consistency and tend to float. This is known as steatorrhea.

Artificial Sweeteners

Artificial sweeteners are often used when dieting to reduce the calorie intake as compared to regular sugar. However, artificial sweeteners can cause diarrhea for several reasons. It depends on the constituents of the sweetener. Some people are unable to intolerant to substances like sorbitol or fructose which may be the main ingredient in certain sweeteners. As a result these substances remain in the gut and bowels thereby affecting water secretion and reabsorption. It leads to watery diarrhea.


Supplements that are used when dieting can also contribute to diarrhea. This may include nutritional supplements (vitamins and minerals) in very large doses, supplements with laxatives and supplements with stimulants. Energy drinks and certain teas that may be used as part of weight loss program can also contribute to diarrhea for several reasons like disturbances in the fluid levels in the bowels as well as increased bowel motility.


The change in diet with weight loss eating plans may adversely affect the normal intestinal flora. This is the bacteria and fungi that naturally reside in the bowels, specifically the colon, and play an important role in digestion and absorption. When the normal intestinal flora is disturbed then it can lead to bowel symptoms like diarrhea or predispose the bowels to infections which may then cause diarrhea.

Read more on diarrhea FAQ.

Remedies for Diarrhea When Dieting

If the cause of the diarrhea is not associated with the dieting, then this underlying cause needs to be treated and managed. It is therefore important to consult with a doctor. Antidiarrheal drugs should not be the first option for managing the diarrhea. However, if the diarrhea is caused by the dietary changes then the following measures may help.

  • Use an oral rehydrating solution (ORS) which is usually available as granules which must be dissolved in water. Avoid fruit juices, energy drinks, tea, coffee and/or alcohol.
  • Consume moderate amounts of fiber, preferably in foods like fruits, vegetables and wholegrains. In moderation, these foods may not substantially increase the daily calorie intake.
  • Include live culture yogurt and other foods rich in probiotics. This will help to restore the normal intestinal flora (“good bowel bacteria”). Probiotic supplements may also be helpful.
  • Do not eat very large meals after long periods of no food intake. It is better to opt for several small meals throughout the day that still maintains the required calorie intake for weight loss.

Please note that any information or feedback on this website is not intended to replace a consultation with a health care professional and will not constitute a medical diagnosis. By using this website and the comment service you agree to abide by the comment terms and conditions as outlined on this page